[56.02] Soft Gamma-ray Repeaters

C. Kouveliotou (USRA at NASA/MSFC)

Soft Gamma Repeaters (SGRs) are sources of brief intense
outbursts of low-energy \gamma radiation, which occur in
bunches, with active periods lasting between few weeks and
several months at time intervals of years. Three SGRs were
discovered between 1979 and 1983 and a fourth in 1998. Their
(rudimentary) sky distribution (three very close to the
galactic plane in the central regions of the Galaxy, the
fourth in the LMC) indicates that peak luminosities of SGR
bursts are in the range 1042 to 1044 erg/s and
suggests that SGRs are a young source population, a
conclusion supported by the stregthening association of SGRs
with young supernova remnants.

In early 1998 we discovered X-ray pulsations from two SGRs:
SGR~1806-20 and SGR~1900+14, with periods of 7.47 and
5.16 s, respectively. Subsequent observations revealed a
significant spindown of these periods, of the order of
10-10 s/s in both cases. The P and \dot{P}
measurements allowed us to conclude that SGRs are magnetars,
i.e., young neutron stars with very strong magnetic fields
of B>1014 G. I will describe the SGR overal
characteristics and discuss the evidence that link SGRs to
magnetars.